Key to Species Groups and Subgroups of Taxus

1. Leaf epidermal cells angular in T-sect. (Fig. 15), papillose on the abaxial (ventral)
midrib; North America (SE Alaska and W Florida) to Central America (Honduras,
El Salvador), Himalayas, SW China...............................................
.........................................................................—I. Wallichiana Group (Wallichiana Subgroup)

1. Leaf epidermal cells ±elliptical or wide rectangular in T-sect.,1.5–3.5 times as wide
as tall (Fig. 16), variable in development of midrib papillae—2

     2. Stomata bands in dried leaves not sharply differentiated
      from adjacent marginal and midrib regions, the abaxial surface
      uniformly green to yellowish green or reddish or paler green on
      midrib and marginal zones...................................................................................... —3

2. Stomata bands distinct in dried leaves by glossy margins and
midrib, the margins and midrib often discolored—reddish (Fig. 17).......................—4

3. Leaves with resinous cells primarily epidermal; papillae ± equally developed
across stomata bands and midrib (Fig. 18), often more prominent along cell walls;
stomata sometimes on midrib, bands with (11-) 13–19 (-21) rows;
E Himalayas to S China ......................................—II. Wallichiana Group (Chinensis Subgroup)


Fig. 18. Abaxial surface of fresh leaf of T. globosa, from Oaxaca, Mexico, showing stomata above (Fig. 18a), papillae on midrib below (Fig. 18b), 250×.
	Fig. 19. Leaf stomata (left) and midrib (right, 400×), Taxus caespitosa, from South Korea. Papillae are prominent in T. globosa (Fig.18) along cell walls and on surface in an alternate arrangement, whereas here in T. caespitosa papillae appear more fused together (concrescent) to form low ridges, or thickened walls on midrib cells (right).

3. Leaves with resinous (oil) cells primarily in mesophyll; papillae often less developed
on midrib (Fig. 19) than on stomata bands, or more medial than marginal (T. baccata
Alliance, Euro-Mediterranean, W Himalayas), or papillae reduced along cell
walls—appearing concrescent (T. cuspidata Alliance, NE temp. Asia); stomata
in bands only, stomata (4-) 5–7 (-9) rows in NE temp. Am., (4-) 8–10 (-15) rows
in Euro-Medit., (7-) 9–14 (-16) rows in temp. E Asia....................................—IV. Baccata Group

4. Abaxial leaf epidermal cells meeting at sharp angles, mostly smooth on midrib and
marginal regions—from 8–36 cells across; papillae more medial than marginal;
stomata rarely in transverse rows; E Himalayas to Indonesia................ —III. Sumatrana Group

4. Abaxial leaf epidermal cells fusiform to narrowly rectangular on midrib,
meeting at rounded angles, mostly papillose except for (0-) 2–6 (-12)
cells nearest margins and outer midrib region, the papillae marginal; stomata
often in transverse rows; E Himalayas to Indonesia................................II. Chinensis Subgroup